Poachers shot dead and de-horned a male rhino in India’s Kaziranga national park less than 10 hours after the Duke and Duchess of Cambridge enjoyed a jeep safari there during a visit to highlight conservation, Indian media has reported.

The royal couple visited Kaziranga in Assam and the nearby Centre of Wildlife Rehabilitation and Conservation (CWRC) on Wednesday, and were staying around 12 miles (20km) away at the time of the incident at around 11.10pm.

“Our forest guards who rushed to the spot on hearing gunshots were engaged in an exchange of fire with the poachers, but the culprits managed to escape under the cover of darkness,” the Kaziranga divisional forest officer Subhashis Das told the Indian Express.

The Duke and Duchess of Cambridge look at a rhino in Kaziranga national park. Photograph: Adnan Abidi/AP

It is said to be the sixth rhino killed by poachers in the 480 sq km park this year.

It was reported that as many as 105 empty cartridges from AK-47 weapons were found strewn near the spot. The paper quoted sources saying ordnance factory marks on the cartridges had fuelled suspicions that the weapons could have been among those snatched from security forces by rebel groups in the adjoining Karbi Anglong district.

Kazinranga is home to more than 2,400 one-horned rhinos and poaching has become a major issue.

Additional security was deployed during the royal visit, during which the couple helped feed rhino calves with bottled milk at the CWRC sanctuary.

Another rhino had been killed by poachers three days before the arrival of the duke and duchess. Prince William was said to be appalled when shown footage of its mutilated remains. He spoke to the head of the park about the issue and is to help fund training and equipment for rangers through his charity United for Wildlife.

The Duke and Duchess of Cambridge are taken on open-top safari and spend a day with rhinos and elephants at the Centre for Wildlife Rehabilitation and Conservation in Kaziranga national park, as part of their tour of India and Bhutan

The Duke and Duchess of Cambridge are on a week-long visit to India and Bhutan. They have met India’s prime minister, Narendra Modi, as well as an elderly man who may well be the nation’s No 1 royal fan